Theory
Usability
This page looks at usability in the context of web design.
Reading vs Scanning
People do not read websites, they scan them, so we need to design with that in mind, breaking text into paragraph chunks, and using headings so visitors can see what the text is about quickly.
Muddling Through
Also it is clear from studies that users do not figure out what is on the web page, they "muddle through", quickly trying to find the stuff they need.
First Reasonable Plan
How they decide what to do on any given website is that they look quickly, then launch the first reasonable plan they can come up with.
Headings
A clear, h1 heading for every page helps the visitor understand where they are at any time.
Conventions are Useful
Conventions, such as having a main menu at the top of the page, are our design "friends", because they help us to guide the user. The user knows where to look for such things because of past experience which used the same conventions.
Buttons that look like...
If the user ever has to ask themselves "is that a button", then it is likely because of poor navigation design. A button should look like a button, and it should act like a button.
Related Functions Related Visually
When laying out the page, parts of the page that are related logically (for example, the main menu), should be related visually (by being the same color, being in the same general area, using the same font, and so on).
Too Much Stuff is Bad
Too many elements on one page makes the page busy (this is called "noise"). Too much noise is distracting, and makes decision-making harder for the user.
Number of Clicks
As the user navigates the site, it might take two or five clicks to get to what they are looking for. What is critical here is not the number of clicks, but how hard each click is to figure out.
Hierarchy in Design
When designing a website, the users are in such a hurry that it can be compared to driving by a billboard at high speed. So, we need to design our sites as if they are billboards, using hierarchy - that is, the most important stuff should be bigger and come first, and the least important stuff should be smaller and lower in the frame.
Persistent Navigation
The site navigation should be persistent, that is, it should almost always be the same on every page, so users can find and use it quickly. The exception to this might be cases such as the home page where it may appear bigger or differently, or a page that uses forms like the contact page.
Teleporting
Clicking on buttons and instantly going to different places is like teleportation, because we don't see the relationship between where we were and where we are like we do when we walk or drive between two locations. So we need to help the user see where they are each time they arrive at a page. One way to do this is with "current page" menus that show what page you are currently on by highlighting or changing the color of that menu selection; another way is by using headings at the top of each page that describe the contents of that page - when these are used, they should be prominent and well-placed on the page.
Sameness in Link and Destination
When the user clicks on any given page, for example a page called "Tools", they should end up on a page with the same name or heading, not on a page called "Equipment" or something else. Changing terms in the midst of navigation is confusing to users.
Pull-Down Menus are Good and Bad
Pull-down menus are good in that they save space, but bad in that they hide valuable information from the user, and can be "twitchy" in that they sometimes don't work well or can disappear too quickly for the user to use them properly.
Taglines
The site should have a good tagline, which gives the site branding and characterises the enterprise.
The Home Page
The buttons that leads to the home page should be in sight at all times, and the home page should explain what the site is, and what the user can do here.
A Worthy Book
Some of these ideas were adapted from
Don't Make Me Think: A Common Sense Approach to Web Usability, 2nd Edition